This program of research investigates the ability of mildly mentally retarded adults to perceive and process correctly certain classes of stimuli with distinctive attributes. Included are global stereoscopic forms, global kinetic forms, patterns of biological motion and size/distance interactions produced by 3-D space. These stimuli engage preattentive processes early in the visual system and are seen effortlessly by nonretarded persons. However, prior research has demonstrated that such stimuli reveal substantial perceptual deficits in mildly retarded persons under conditions that eliminate, as contributing factors, peripheral visual anomalies and failures of comprehension. This is a surprising outcome because mild retardation is generally regarded to be a product of intellectual and cognitive deficiencies. The proposed inquiry seeks to specify more precisely the characteristics of these perceptual deficits. The resulting data should contribute directly to a deeper understanding of mental retardation. More generally they bear on the issue of the separability of cognitive and perceptual processes.